Low energy availability: history, definition and evidence of its endocrine, metabolic and physiological effects in prosp
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INVITED REVIEW
Low energy availability: history, definition and evidence of its endocrine, metabolic and physiological effects in prospective studies in females and males José L. Areta1 · Harry L. Taylor1 · Karsten Koehler2 Received: 31 July 2020 / Accepted: 23 September 2020 © The Author(s) 2020
Abstract Energy availability (EA) is defined as the amount of dietary energy available to sustain physiological function after subtracting the energetic cost of exercise. Insufficient EA due to increased exercise, reduced energy intake, or a combination of both, is a potent disruptor of the endocrine milieu. As such, EA is conceived as a key etiological factor underlying a plethora of physiological dysregulations described in the female athlete triad, its male counterpart and the Relative Energy Deficiency in Sport models. Originally developed upon female-specific physiological responses, this concept has recently been extended to males, where experimental evidence is limited. The majority of data for all these models are from crosssectional or observational studies where hypothesized chronic low energy availability (LEA) is linked to physiological maladaptation. However, the body of evidence determining causal effects of LEA on endocrine, and physiological function through prospective studies manipulating EA is comparatively small, with interventions typically lasting ≤ 5 days. Extending laboratory-based findings to the field requires recognition of the strengths and limitations of current knowledge. To aid this, this review will: (1) provide a brief historical overview of the origin of the concept in mammalian ecology through its evolution of algebraic calculations used in humans today, (2) Outline key differences from the ‘energy balance’ concept, (3) summarise and critically evaluate the effects of LEA on tissues/systems for which we now have evidence, namely: hormonal milieu, reproductive system endocrinology, bone metabolism and skeletal muscle; and finally (4) provide perspectives and suggestions for research upon identified knowledge gaps. Keywords Energy availability · Energy balance · RED-S · Triad · Exercise · Nutrition Abbreviations AMPK AMP-activated protein kinase β-CTX β-Carboxyl-terminal cross-linked telopeptide of type I collagen β-HOB β-Hydroxybutyrate CIT Cold-induced thermogenesis DIT Dietary-induced thermogenesis E2 Estrogen EA Energy availability Communicated by Michael Lindinger. * José L. Areta [email protected] 1
Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Tom Reilly Building, Byrom St Campus, Liverpool L3 3AF, UK
Department of Sport and Health Sciences, Technical University of Munich, Munich, Germany
2
EEE Exercise energy expenditure EI Energy intake FSH Follicle stimulating hormone GH Growth hormone IGF-1 Insulin-like growth factor 1 LBM Lean body mass LEA Low energy availability LH Luteinizing hormone MPS Myofibrillar protein synthesis NEAT Non-exercise activity thermogenesis NTx N-terminal telopeptide of type 1 col
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